A desire to increase the speed and density of integrated circuits (ICs) has led to transistor scaling accompanied by progressive reductions in the thickness of the gate oxide. A thinner gate oxide provides greater drive current, thereby increasing speed. Also, a thinner gate oxide provides greater control over the channel charge, thereby reducing short channel effects. However, thinner gate oxides present greater problems of manufacturability, quality, and reliability.
One way to avoid the problems of a thinner gate oxide but achieve the desired capacitive effect is to replace the gate oxide with a gate dielectric that has a greater dielectric constant than silicon dioxide. Paraelectric materials have dielectric constants that are usually at least two orders of magnitude above that of silicon dioxide, but several problems limit their use as gate dielectrics. One such problem is illustrated in FIGS. 1a and 1b. FIG. 1a is a cross sectional illustration of a prior dielectric system before any high temperature processing has occurred, such as source/drain dopant activation, and FIG. 1b is a cross sectional illustration of the same dielectric system after high temperature processing has occurred. During these high temperature processes, oxygen diffuses from gate dielectric 101 to interface 102 between gate dielectric 101 and gate electrode 103, and to interface 104 between gate dielectric 101 and channel 105. The diffused oxygen forms oxide layer 106 at these interfaces, decreasing the overall capacitance of the dielectric system and partially counteracting the effect of the high dielectric constant paraelectric material.
Therefore, a better way to form a high dielectric constant insulator in the fabrication of an integrated circuit is desired.